In the United States alone, there are more than 30 million adult runners. To maintain proper body temperature, runners sweat. The water in the sweat needs to be replaced. Appropriate hydration is critical for runners, particularly those who are running for a long period of time. Improper hydration is one of the most common reasons why marathon runners require medical attention during races.
Dehydration causes numerous problems. Even being at one-percent dehydration can affect a runner's performance. For example, a one-percent dehydration may lead to a 10% decrease in performance, which can translate to about 1-hour delay over an extended race, such as a triathlon. In other words, a relatively small fluid loss, such as one pint, can decrease athletic performance by 10-15%. In addition to diminished performance, symptoms of dehydration include thirst, irritability, headache, weakness, dizziness, cramps, chills, vomiting, nausea, and head or neck heat sensations.
The severely dehydrated can go into shock and end up losing control of all of their bodily functions. Though terribly thirsty, they cannot drink. Even ice chips in their mouths might make them vomit. At that point, to replenish the lost fluids, they need to have fluids applied intravenously.
Dehydration is not the only problem. Over-hydration can be problematic as well. Runners lose not only water, but also a certain amount of sodium and other minerals while sweating. Runners can consume large quantities of water during their races. This can cause a drop in overall sodium levels and, potentially, hyponatremia, which means low levels of salt in the blood. The problem typically arises when the runner runs for a long duration of time, such as three hours, while drinking only plain water.
The human body plays a delicate balancing act with the concentration of sodium in the blood. Small changes in the balance can be dangerous to a body's osmotic chemistry. Almost every physiological process in our body depends on osmotic gradients, with water moving from an area of lower salt concentration to an area of higher salt concentration. Severe sodium imbalance may lead to seizures, increased intracranial pressure, pulmonary edema (fluid in the lungs), respiratory arrest and even death. Many scientists view hyponatremia being as threatening to runners as dehydration and heat sickness.
To prevent dehydration or over-hydration, one approach is to drink the amount of fluid substantially equal to the sweat and urine losses.
Sometimes thirst may be a good indicator as to when to drink. If you are thirsty, drink. Monitoring the volume and color of urine can be helpful in determining hydration status as well. A general guideline is to drink until your urine is clear. However, by the time you feel thirsty, for example during a workout, you may already be dehydrated. Also, in the heat of a race, a runner may forget or suppress the natural instinct of thirst and not check his urine.
Another approach to determine when to drink is to measure one's body temperature. One recent approach is to swallow a small temperature sensor. However, some athletes may not want to swallow such a foreign object.
One recommendation from a number of marathon associations is to weigh runners prior to a race and again following the race. The drop in weight post-exercise could provide an indication as to roughly how much fluid one needs to replenish. In the heat of a long race, it may not be convenient to weigh oneself during the race. Also, runners must exercise care when stopping to weigh themselves in the middle of a race. Postural hypotension is experienced when a runner suddenly stops. Blood pooling in the legs can lead to inadequate blood supply to other parts of the body. The runner can then feel faint and collapse.
Although running has been used above as an example to illustrate the importance of proper hydration, proper hydration is important in other types of sports, particularly for endurance sports or sports lasting for a long duration of time. The challenges not only fall on the adults, but children as well.
Hydration is also an issue in children. It can be quite difficult to determine whether a toddler is sufficiently hydrated. We cannot depend on whether he is crying or not. He can be distressed for numerous reasons, and the basic reason may not be easily decipherable. The difficulty is exacerbated if the toddler has diarrhea and is vomiting. Typically, particularly for first-time parents, they often take the toddler to a healthcare provider.
It should be apparent from the foregoing that there is a need for ways to determine if a person is appropriately hydrated. Furthermore, it is desirable that the ways be applicable to people of different ages and in different conditions. Also, it would be helpful if at least some of the ways are affordable so that people with limited means can still use them.